Bone conduction hearing aid



June 21, 1949. f

H..KocH

` BONE CONDUCTIQN BBARIHGAID f' Re. 23,125-

ongxnal FundA Deo. 451,' 1941;

YIIII". 'A

IN VEN TOR.

Reissued June 21, 1949 BONE CONDUCTION HEARING AID Henry Koch,Huntingdon, Pag, assignor to Dictograph Products Company, Inc., NewYork,N. Y., a corporation of Delaware Original No. 2,405,433, dated` August6, 1946, Serial No. 425,039, December 31, 1941. Application forV reissueJune 28, 1947, Serial No, 757,799

Claims. l.

This inventicnrelates to' audiphones and has particular reference toaudiphone lreceivers having a vibrating contacter adapted to be placedin operative connectionwith the bonestructure of the user fortransmitting audible sounds picked up by a suitablel microphone to theinner ear through the bone structure.

Bone conduction receivers may be divided'into two general classes,direct actingeand reaction. In the former the bone contacter is directlyconnectedtoA the vibrating'element, such as a reed, of7 anelectromagnetic system, the magnet structure of'whieh is held relativelystationary by a headband or the like, so that the contacter Vibratesrelatively thereto. In the reaction type of receiver, theA bone engagingcontacter connected to thefvibrating element, such as a reed,issupported-by-aheadband or the like, so that the electromagnetic systemhangs free and, inasmuch as this system hasV substantial mass7 itremainsstationary While the contactor vibrates relatively thereto byfreaction.

Each class of bone conduction receiver has certain advantages over theother, as Well as certain disadvantages. Thus, inasmuch as the reactiontype of receiver vibrates bodily as a unit, itz necessarily alsovibrates thefconnectingv portion of the headband as well, whichimposesvsomerestraint on, the vibration-requiring increased mass againstwhich the reed may react, thus requiring considerable power foroperation.

The direct acting bone receiver does not require vibration of theheadband since only the reed.. and contacter Aare-fvibrated, but thenecessary: pressure of. the contacter against the bone in orderfto-obtain good conduction is considerable, and that results insuppression of the reedk or.` diaphragm towhichy the contacter isconnectedand variation of theair gap.l This objection Vto direct-actionreceiverslis-largely overcome in the improvement disclosed in my PatentNo. 2,144,458, in Whichn the contacter, forming part of the casingwallengaging the` body, is carried byy the reed, Which.is=made sufficientlystiff tov the,` stili reed cannot. withstand this abnormaly pressureandf-isvlexed With consequent variance' of the air gap and ineicient andineffective re production. In one formof the invention of my .sa-idpatent, resilient' material', such as rubber or felt is interposedbetween the -contactor and' the casing carrying the magnetic structureso thatv even under abnormal pressures onthe contactor` the air gapisnot varied sufficiently to impair operation of the device. However, eventhough this cushion is resilient, it aiects'normal electromagneticvibration and is-not entirelyl satisfactory.

The-present invention is concerned with im provements on the'direct-acting bone receiver disclosed in mysaid'P'atent No. 2,144,458,in which the general characteristics of the receiver there disclosed areretainedan-dthe disadvantage ofv susceptibility tov abnormal pressuresof the contactorf againstthe head is eliminated. Thisv is accomplishedin a preferred embodiment" of the present inventionby resilientlymounting the entire magneticstructure in the casing by springmeans-softer or less resistant to flexingy than the stiff reed', i; e.,which will flex beforethe reed'flexes; under abnormal pressures, sothaty the entireelectromagnetic system floats Within the casing to berestored'to its normal position by the, spring means when the abnormalpressure is released,` Without impairment in its operation during theperiod of abnormal pressure;

The receiver of thisinvention is also preferably mounted directly on theheadband which lies flatwise against the-head-so -that anyy pressureagainst the headband will not change thepositionof theelectromagneticstructure resiliently supportedwithinthe casing inthemanner described.

Fora more-.complete understanding of the invention; reference mayv behadto the accompany'- ing drawing, in which:

Figurewl illustrates theY bone conduction receiver of this inventionsupported cna headband;

face plate for the receiver VAL as-I it-is held llatwisel against thehead. Projecting-slightly beyond ,the surface'of theiace -plate Il is abone-engaging contactor` or button' I2;- which is vibrated'by'electrica-l means Withirrthecasing lll'so-as to transg mit itsvibrations through the intervening bone to the inner ear of the user.The electrical means is energized by voice currents picked up by asuitable microphone I3 in circuit with a battery or other source ofpower I4 and preferably a vacuum tube or carbon booster amplifier, notshown, connected to the electrical means within the casing A by thefiexible electric cord IE having the separa-ble plug type connectors I6plugged into the casing Ill.

The aforementioned electrical means Within the casing i Il may beelectromagnetic, a piezo-electric crystal, or any other means responsiveto energization by voice currents to produce sufciently powerfulvibrations for intelligible transmission through the bone to the innerear. Electromagnetic means are shown in the drawings by way ofillustration of the invention, and in Fig. 2 comprises a bar magnet Iiresiliently supported within the casing Ii] by means of a leaf spring I8secured at one end thereto by screws I9 and at its other end to the faceplate II, as by bolts countersunk in the face plate II.

Also secured to the same end of the bar magnet I'I is the reed 2|,having a generally L shape and forming at its free end a narrow air gap22 with the opposed end of the pole shoe 23 secured to the other end ofthe bar magnet I by screws 26| and carrying the voice coil 25. The reed2| and the magnet IT are free of and spaced from face plate II andcasing I0, respectively.

- VoiceI coil 25 is connected to connector plugs it by filaments 26soldered to studs 2'I on concluetor plates 2t insulated from headband II and connected through springs 29 and friction buttons 3i? to the plugsI6.

i Secured to the free end of the reed 2| is a contactcr button I2 whoseouter surface projects only slightly beyond the skin engaging surface offace plate I i'. For a small area contactor I2 as shown such slightprojection is desired in order that the skin beneath it will becompressed slightly more than the surrounding skin beneath the faceplate I I, so that the skin is firm and hence more conductive of thevibrations at the point of application thereof.

The average degree of skin compressibility, over the mastoid eminence,for example, is such that the projection of the contactor I2 beyond theface plate I I need not exceed from V64 to 1/aa of an inch, so that thebutton is substantially flush with the face plate'. The degree ofprojection of the contactor in the drawings is shown exaggerated in theinterest of clarity. It will be understood that where the contactorconstitutes a large part or all of the area of the face plate, as shownin my aforementioned patent, there will be less cr no projection of thecontactor beyond the face plate, because the need for localized skincompression decreases as the area of the contactor increases.

The contactor I 2 extends through a hole in the face plate II', which issufficiently oversize that there is no contact between the contactor I2and the face plate I I. The consequent narrow annular slot around thecontactor I2 is sealed by a ring of felt 3| against ingress of moisture,dirt and the like, this ring 3| being clamped between the contactor I2and the reed 2|.

The air gap 22 has a width on the order of a few thousandths of an inchand the reed 2| is thick and consequently stiff, so that a force on thecontactor I2 in excess of normal headband pressures, i. e., greater thanabout five ounces, is necessary in order to deflect the reed 2|suihciently to affect the air gap 22. Thus, if the stiffness selectedfor reed 2| is such that a force of eight ounces is necessary to deflectit at the air gap, the stiffness of spring I8 is made such that itflexes before the reed 2I is flexed, e. g., when a pressure in excess ofsix to seven ounces is applied to the contactor I2. These degrees ofstiffness are predicated on normal headband pressures in theneighborhood of ve ounces, so that a pressure in excess thereof isabnormal. Obviously, if the normal headband pressure is greater or lessthan that in the given example, the reed 2| will be made stiffer orsofter, as the case may be, and spring IB will always bemade to iiexunder a contactor pressure somewhat less than that required to deiiectthe reed 2|.

In operation of the bone conduction receiver illustrated in Figs. 1 and2, the face plate I I' is held firmly against the head, such as on themastoid eminence, by the headband II, with a normal pressure of fiveounces. The contactor I2 does not move under this pressure because thestiffness of the reed 2| is such that a greater pressure is required onthe contactor IZ before the reed is flexed. Consequently the contactorcompresses the skin beneath it slightly more than does the surroundingskin-engaging portion of the face plate I I', so that a firm vibrationconducting coupling between it and the bone is provided. Energization ofthe electromagnetic system results in vibration of the contactor I2relatively to the headband Ii and casing I0 and transmission of itsvibrations through the intervening bone to the inner ear.

n If the pressure on the contactor I2 is increased abnormally, as whenthe user presses on the casing III while it is on his head, or presseshis linger on the contactor I2 while the receiver is not on his head,the spring I8 will flex, allowing the contactor I2 to recede into thecasing, the entire magnet system moving therewith without any flexing ofthe reed 2|. Even when the device is in use and the casing is pressedagainst the head or a tight hat placed over the headband II producing asimilar effect, the operation of the receiver is not impaired.

By securing the casing ID to the headband Il, as shown, so that a largearea of the latter engages the head, the effect of pressure on theheadband, as by a tight hat, is minimized and usually precluded. Thisadvantage is not possible with headbands of the pivoted fork type shownin my said patent, where the headband is spaced from the head and henceis more susceptible of movement and consequent suppression of thecontactor under abnormal pressures. It will be understood that thisarrangement of headband co-extensive with or continuous with the faceplate may be employed with advantage on any type of bone receiver, suchas those described in my said patent.

in the modified form of the invention shown in Y Fig. 3, the bar magnetI7 is suspended by a spring I8 from the inside vof the casing I to whichspring I8 is secured by bolts 32 located opposite the center of themagnet Il'. Secured to opposite ends of magnet I'I by screws 33 is aU-shaped spring 34 carrying at its center the armature 35 screwed tocontactor I2', which may be a hard rubber button or other non-metallicmaterial. Pole shoes 23 also secured to the ends of the bar magnet I`|by the screws 33 form narrow air gaps with the armature 35 and carry thevoice coils 25 connected in the :microphone` i circuit through'filaments 26', bushings 3.6, 4and connectors i6'.

The contactor projects slightly beyond-thesurface of the face platel-I", whichis coextensive lwith the headband Il, and a felt washer 3'l flseals Vthe annular space rbetween the perimeter of the contactor l2andthe hole thereforin the face plate H. As before, the spring 34, which'corresponds tothe reed 2l of Fig. 1 as a spring, 'is sumciently stiffthat it tdoes not flex -under pressures of button l2' on the ybone equalto normal -or 'slightly greater, depending upon requirements. However,spring 't8' is softer than "spring 34, so that itilexes under abnormalpressures on contacter l2', allowing the entire'velectromagneticstructure to move vinwardly until vvequilibrium is obtained. When thepressure is "released the system is restored by spring -|8-, withoutimpairment of the operation of the receiver during this interval ofabnormal pressure. 'The arrangement of Fig. 3 differs from that of Fig.2 in that the -ux paths Yare shorter and `the movement under abnormalpressure is in the direction of the-pressure vinstead of aboutsprin'gI-B' as a form of pivot in Fig. 2. The operatic-n is the samein'each'case.

It will be seen that the present invention pro- `videsa simple andeffective solution to the problem of operation of bone conductionreceivers, while preserving the advantages thereof, and -while certainpreferred embodiments of the invention have been illustrated and`described herein, it is to be understood that they are merelyillustrative and do not llimit'thein'vention Within the 'scope of theclaims.

I claim:

l. In an audiphone receiver, the combination of an electromagnetic meansadaptedfto `respond to varying currents substantially throughout theaudible frequency range, a casing having a face plate adapted Atoengagethe'body of the user, a contactor forming at least part of thebodyengaging surface of said face plate and vibrated by saidelectromagnetic means relatively to said casing, relatively stiff springmeans connecting said contacter and electromagnetic means, and resilientmeans connecting said electromagnetic means directly connected to saidcasing and supporting said electromagnetic means, spring means andcontactor for bodily movement of the same as a unit relatively to saidface plate in response to excessive pressures applied to said contactor,said resilient means having a stiffness less than that of said springmeans.

2. In an audiphone receiver, the combination of an electrical meansadapted to respond to varying currents substantially throughout theaudble frequency range, a casing having a face plate adapted to engagethe body of the user, a contactor forming at least part of thebody-engaging surface of said face plate and vibrated by said electricalmeans relatively to said casing, relatively stii spring means connectingsaid contactor and electrical means, means supporting said face plateand contacter in simultaneous connection with the bone structure of theuser with a predetermined pressure less than that required tosubstantially flex said spring means, and resilient means directlyconnecting said electrical means to said casing and supporting saidelectrical means, spring means and contactor and said supporting meansfor bodily movement of the same as a unit relatively to said face plateunder pressure on said contactar greater than said predeterminedpressure.

3. 'In an audiphone receiver, ithe @combination 'of an electrical meansadapted to respond to varying currents vsubstantially @throughout thevaudible frequency range, afcasng enclosing 'said electrical means, aheadband secured 'to ysaid casing and forming -a wall thereo'fengagingthe body of the user with a predetermined pressure,

vresilient means .directly connecting =said electrical 'means to said'casing ifor bodily movement relat1vely thereto, said resilient meanshaving `a stiffness precluding substantial yflexing under contactcr'tosaid electrical'means and Vhavinga.

stiffness greater thantliato'f said resilient means, kwhereby pressurer'on said contactor in excess o said predetermined 4pressure causes'flexing 'of said resilient means and bodily movement "of saidelectrical means, spring means and contactor as a'unit relativelyvtosaid casing.

4. In an audiphone =receive1, lthe combination of an electrical meansadapted to respond to Varying currents substantially throughout theaudible frequency range, a 'headband having a relatively iiat portionadaptedtofengage'the head of the user, a casing I'-for --saidfelectricalmeans having a wall coextens'ive with said headbani portion, and acontactor `vibrated `vby said electrical means and .adapted to engagethe Ihead of the user simultaneously --W'ith said headband portion.

5. In an audipho'ne rleceiver, the combination of an electrical means`adapted to respond -to varying currents substantially throughout theaudible frequency range, `a "headband -having 'a relatively iiatVportion adapted toengage thehead of the user, a contactor vibratedbylsaid electrical means and substantially 1flush with said headh bandportion for transmitting its vibrations through the bone to the innerear, and a casing for said electrical means mounted on said headband.

6. In an audiphone receiver, the combination of electro-magnetic meansadapted to respond to varying currents substantially throughout theaudible frequency range, said electromagnetic means comprising a unitincluding a magnet structure, voice coil, vibratory armature, arelatively stiff spring connecting said armature and magnet structureand a contacter connected to said armature for Vibration therewith, acasing for said electromagnetic means, said contacter forming at leastpart of a wall of said casing, resilient means directly connecting saidmagnet structure to said casing and having less stiifness than saidspring, whereby excessive pressure on said contacter-causes saidresilient means to ex to permit bodily movement of said electromagneticmeans as a unit relatively to said caslng.

'7. In an audiphone receiver, the combination of electromagnetic meansadapted to respond to Varying currents substantially throughout theaudible frequency range, said electromagnetic means comprising a unitincluding a magnet structure, voice coil, vibratory armature, arelatively stiff spring connecting said armature and magnet structureand a contacter connected to said armature for vibration therewith, aheadband having an aperture for said contactor, a casing for saidelectromagnetic means mounted kon said headband, said headband forming awall ,of the casing, and resilient means directly connecting said magnetstructure to said casing and having a stiffness less than said spring,whereby said electromagnetic means moves bodily as a unit in said casingin response to excessive pressures on said contactor.

8. In an audiphone receiver, the combination `of electromagnetic meansadapted to respond to varying currents substantially throughout the`audible frequency range, said electromagnetic `means comprising a unitincluding a magnet structure, voice coil, vibratory armature, arelatively stiiT spring connecting said armature and 4magnet structureand a contactor connected to said armature for vibration therewith, aheadband having an aperture for said contactor, a casing for saidelectromagnetic means mounted on said headband, said headband forming awall of the casing, and a second spring directly connecting said magnetstructure to said headband and affording bodily movement of saidelectromagnetic means as a unit relatively to said casing yin adirection opposite to that of application of the contactor to the bodyof the user, said second spring having less stiiness than said iirstspring.

9. In an audiphone receiver, the combination of a vibrating mechanismcomprising two members, relatively stil spring means connecting saidmembers and permitting relative movement between at least portionsy ofboth members, electrical means adapted to respond to varying currentswithin the audible frequency range secured to said portion of one ofsaid members and operatively opposed to said portion of the other memberfor relatively vibrating the latter, a contactor .connected to the saidportion of said other member for vibration therewith, a resilientheadband for holding said contactor rin engagement with the body of theuser with a predetermined preslsure, and a leaf spring having lessstiffness than member to and supporting the same on said headband,whereby the said portion of said member and the contactor are free tovibrate relatively to said other member and the headband and said leafspring iiexes to permit bodily movement of said vibrating mechanism andcontactor relatively to said headband in response to excessive pressureon said contactor without suppressing the vibration of said portion ofsaid one member and contactor.

10. In an audiphone receiver, the combination of a vibrating mechanismcomprising two members, relatively stiff spring means connecting saidmembers and permitting relative movement between at least portions ofboth members, electrical means adapted to respond to varying currentswithin the audible frequency range secured to said portion of one ofsaid members and operatively opposed to said portion of the other memberfor relatively vibrating the latter, a contactor connected to the saidportion of said other member for vibration therewith, a resilientheadband connected to the said portion of said one member and having anormal stiffness less than the stiffness of said spring means forholding said contactor in engagement with the body of the user with apredetermined maximum pressure, and a spring directly interposed in saidconnection between said headband and the said portion of said one memberand having greater stiness than said normal stiffness of said headbandbut less stiffness than said spring means, whereby pressure of saidcontactor in excess of said predetermined maximum pressure causes saidspring to iiex and permit bodily movement of said vibrating mechanismand relatively to said headband without affecting said spring means.

HENRY KOCH.

No references cited.

